DESCRIPTION (Adapted from applicant's abstract and specific aims): The overall objective of this revised AREA grant is to study regional differences in muscularis mucosae innervation and pharmacology in three different species, opossum, rabbit and rat. The proposed work will utilize techniques developed by the applicant to address three specific aims: 1) to characterize the nature of the neurotransmitters released by the nerves of the submucosal plexus innervating the muscularis mucosa in different intestinal regions; 2) to classify the receptor subtypes that mediate the muscularis mucosae responses to the neurotransmitters identified in specific aim #1; and 3) to determine the second messengers that mediate the cellular responses elicited by the engagement of specific neurotransmitters with their receptors on the muscularis mucosae.